Method for creating a high Tensile Strength Joint for Connecting Rods and Fittings

ABSTRACT

A joint exhibits high tensile strength. The joint includes a solid rod having a slit or opening into which a wedge is inserted. The rod and wedge are inserted into a fitting. Only a small amount of adhesive material is applied between the fitting and the rod. The adhesive material may be blended with non-adhesive, non-compressible “beads” that have a preferred diameter in order to insure that the desired adhesive thickness is achieved between the fitting and the rod. The internal surface of the fitting has a contour which continuously and nonlinearly varies with distance along the fitting. The wedge has a dimension having a similar contour. The shape of the contour can be described by a polynomial of order two or higher. The joint can be used to construct a sucker rod for an oil well, or it can be used in other applications. The joint can support high tensile loads, over long distances, while occupying a very narrow tubing bore.

This application is a continuation-in-part of application Ser. No.13/526,782, filed Jun. 19, 2012, and application Ser. No. 16/163,489,filed Oct. 17, 2018.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates generally to connectors and fixtures and, morespecifically, to a High Tensile Strength Joint for Connecting Rods andFittings.

2. Description of Related Art

The present invention comprises a joint which connects a rod and afitting, wherein the rod and fitting are subjected to high-tensionloads. The invention is especially useful in constructing a sucker rodfor oil wells. The invention may be used, however, in many otherapplications, such as in pre-stressed concrete, and in tension membersfor bridges.

A sucker rod is a long rod formed of a plurality of sections, capable ofconnecting a pump, located at the bottom of an oil well, with a liftingdevice, or pump jack, located at the surface. Each section may include arod portion and a fitting portion, each rod being inserted into afitting. In practice, a sucker rod comprises a long chain of rods andfittings and couplings. Because some wells may be deeper than 16,000feet, the sucker rod must have very high tensile strength, so that therod does not break under its own weight plus that of the fluid, as it ispulled up by the pump jack, and pulled down by gravity. The problem ofdesigning a sucker rod having the necessary tensile strength is mademore difficult by the fact that the rod typically must fit within atubing of relatively small diameter.

Various sucker rods have been proposed in the prior art, as exemplifiedby U.S. Pat. Nos. 4,205,926, 4,430,018, and 6,193,431. The disclosuresof these patents are hereby incorporated by reference.

While the above-cited patents provide useful solutions, the patenteddevices have disadvantages. Among other things, some of the prior artuses rods that are made of stranded wire. A stranded rod, by definition,has less than optimal tensile strength, because the strands do notoccupy the entire cross-sectional area of the rod, and the filaments arenot aligned exactly parallel to the rod axis.

In general, the prior art has not developed a sucker rod havingsufficient tensile strength, while occupying a minimal cross-sectionalarea. There is still a need for a sucker rod which is stronger thansucker rods of the prior art, which incorporates advanced materials thatare lighter than metal, and which still fits within a narrow tubingbore.

The present invention provides a joint which exhibits very high tensilestrength, while minimizing the cross-sectional area required. The jointof the present invention can therefore be used to construct longer,lighter sucker rods which can still lift a useful payload of fluid. Itcan also be used in many other applications requiring the assembly ofrods capable of carrying large tensile loads. However, the joint of thepresent invention is not intended to bear significant compression loads.

SUMMARY OF THE INVENTION

In light of the aforementioned problems associated with the priorsystems and methods, it is an object of the present invention to providea High Tensile Strength Joint for Connecting Rods and Fittings.

The present invention comprises a joint which includes a solid rodinserted into a fitting. The rod is preferably a carbon or graphitecomposite, and the fitting is preferably made of steel. The rod has anopening or slit at its ends, into which a wedge is inserted. Theinternal diameter of the fitting varies smoothly and nonlinearly withdistance along the fitting. At the narrow end of the wedge, i.e. the endof the slit where the wedge terminates, the internal contour of thefitting becomes parallel to the axis of the rod. The wedge has adimension which also varies smoothly and nonlinearly with distance.Preferably, the variation of the dimension of the wedge is substantiallythe same as that of the internal diameter of the fitting. That is, thecontour of the fitting is substantially the same as the contour of aportion of the wedge. In a preferred embodiment, this contour can bedescribed by a polynomial function having an order of at least two, suchthat the contour becomes parallel to the axis of the rod at the narrowend of the wedge where it terminates.

In a preferred embodiment, the wedge has a cruciform shape. In a moregeneral case, the preferred wedge includes at least two mutuallynon-parallel vanes. However, the wedge could instead have only a singlevane.

In assembling the joint, the wedge is prepared by forming at least oneslit in the rod, so that the rod can accommodate the wedge. The wedge isthen inserted into the rod, causing the rod to expand or swage outward.When the rod, with the wedge inserted, is inserted into the fitting, thejoint occupies virtually all the space within the fitting, at all pointswhere the rod and wedge are present.

The joint of the present invention exhibits very high strength undertension. The joint may also include a plug which is inserted into thefitting which prevents the rod from being dislodged with respect to thefitting in the presence of relatively small compressive loads.

The joint is particularly suited for use in constructing sucker rods foroil wells, because the joint can accommodate very high tensile loads,while occupying a long and narrow tubing bore. The joint can also beused in applications other than in oil production.

The invention therefore has the primary object of providing a jointwhich exhibits high tensile strength.

The invention has the further object of providing a joint which can beused to construct a long rod, wherein the rod has high tensile strengthwhile fitting within a tubing bore of relatively small diameter.

The invention has the further object of providing a joint for use in asucker rod for an oil well.

The invention has the further object of providing a joint which uses asolid rod, and which thereby takes full advantage of the availablecross-section of the rod, providing a structure of high tensilestrength.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention, which are believed tobe novel, are set forth with particularity in the appended claims. Thepresent invention, both as to its organization and manner of operation,together with further objects and advantages, may best be understood byreference to the following description, taken in connection with theaccompanying drawings, of which:

FIG. 1 provides a perspective view of the joint of the presentinvention, showing a rod inserted into a fitting;

FIG. 2 provides a cross-sectional view of the joint of the presentinvention, taken along the line II-II of FIG. 1;

FIG. 3 provides a side view of a swaged rod, with the fitting removed,used in the present invention, the rod having a cruciform wedge insertedtherein;

FIG. 3a provides a side view of the rod used in the present invention,showing an opening or slit formed therein, before a wedge has beeninserted;

FIG. 4 provides an end view of the rod and the cruciform wedge of FIG.3;

FIG. 4a provides an end view of the slitted rod of FIG. 3 a;

FIG. 5 provides a perspective view of the cruciform wedge used in thepresent invention;

FIG. 6 provides a side view of a swaged rod, with the fitting removed,used in the present invention, the rod having a multiply-vaned wedgeinserted therein;

FIG. 7 provides an end view of the rod and the multiply-vaned wedge ofFIG. 6;

FIGS. 8A, 8B, 8C and 8D sequentially depict the steps of the preferredmethod of the present invention; and

FIG. 9 is a flowchart showing the steps of the preferred method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is provided to enable any person skilled inthe art to make and use the invention and sets forth the best modescontemplated by the inventors of carrying out their invention. Variousmodifications, however, will remain readily apparent to those skilled inthe art, since the generic principles of the present invention have beendefined herein specifically to provide a High Tensile Strength Joint forConnecting Rods and Fittings.

The present invention can best be understood by initial consideration ofFIG. 1.¹ FIG. 1 provides a perspective view showing the joint of thepresent invention. The joint includes rod 1 inserted into fitting 2. ¹As used throughout this disclosure, element numbers enclosed in squarebrackets [ ] indicates that the referenced element is not shown in theinstant drawing figure, but rather is displayed elsewhere in anotherdrawing figure.

In the preferred embodiment, the rod is formed of a composite includinggraphite, or other carbon, and an organic resin. The graphite exists inthe form of tightly-packed fibers or filaments, which maintain theiridentities as having individual, small diameters. The organic resin issimilar to an adhesive, and binds the fibers effectively into a single,solid rod.

In the preferred embodiment, the fitting is a single piece of machinedmetal, preferably formed of high-strength steel. The steel forming thefitting preferably has a yield strength in the range of 110 ksi-140 ksi.The material must not be too brittle, and must allow reasonableelongation (of the order of greater than about 15%) before failure. Thesteel may be selected according to its corrosion resistance properties,if desired.

Although the invention will be described in terms of a graphitecomposite rod inserted into a steel fitting, it should be understoodthat the invention should not be deemed limited to particular materials.It is possible that the rod could be some other material, even metal. Itis also possible that the fitting could be constructed of somethingother than steel, if such material has sufficient strength.

FIG. 2 provides a cross-sectional view of the joint of the presentinvention, taken along the line II-II of FIG. 1. The line II-II issomewhat off-center, as will be apparent later in this description.

FIG. 2 shows solid rod 1 inserted within fitting 2. The rod includes aslit which accommodates a wedge 3. The wedge is inserted within theslit, and occupies substantially all of the space defined by the slit.The wedge therefore causes the rod to be swaged outward. An adhesive 5,indicated symbolically by dashed lines in FIG. 2, is provided betweenthe outer surface of the rod and the inner surface of the fitting, aswell as between the wedge and slit surfaces of the rod.

A plug 4, if included, is screwed into the fitting, with the aid ofthreads 6. The plug provides resistance to small, incidental compressiveforces. That is, if the assembly of rods and fittings is momentarilycompressed, the plug prevents the rod from becoming dislodged andpushing into the open, larger diameter end of the fitting. The plug ispreferably made of metal.

It is an important aspect of the present invention that the wedge besmoothly curved, and that the inside surface of the fitting be smoothlycurved. Also, the curvature of the wedge has substantially the sameshape as the curvature of the interior surface of the fitting.

More precisely, the internal diameter of the fitting varies smoothly andnonlinearly with distance along the fitting. And the wedge has adimension which similarly varies smoothly and nonlinearly with distancealong the wedge.

Thus, as shown in FIG. 2, the fitting has a threaded region, at and tothe right of the plug 4, and a contoured region, to the left of theplug, in which the inside surface of the fitting is contoured asdescribed above.

In one preferred embodiment, the variation of the internal diameter ofthe fitting (as well as the thickness and the width of the wedge) is acubic spline, defined as follows:

D=D _(throat)+2×R _(delta)×[1−1.5(L−z)/L+(L−z)³/2L ³]  (1)

where D is the internal diameter of the fitting;

-   -   D_(throat) the diameter of the rod plus a clearance (typically        about 0.01 inches);    -   L is the length of the contoured internal diameter;    -   R_(delta) is (D_(max)−D_(throat))/2;    -   D_(max) is the desired maximum internal diameter of the fitting        at the point where the width of the wedge is at its maximum; and    -   z is the distance from the start of the contoured shape of the        internal diameter.        Thus, R_(delta) is the increase in the internal radius of the        fitting caused by the swaging effect of the wedge.

The above equation shows that at the start of the wedge, where z=0, thediameter is D=D_(throat). At the right-hand edge of the wedge, wherez=L, the diameter is D=D_(throat)+2R_(delta)=D_(max).

Note also that the slope of the above-defined contour is zero at z=0.That is, the slope of the contour is calculated as the first derivativeof D (equation (1)), as a function of z, and evaluated for z=0. This isanother way of saying that the slope of the contour equals the slope ofthe rod, at the narrow (unswaged) end of the rod, and both such slopesare zero.

The thickness of the wedge, as a function of y, which is defined by FIG.5, is given in the following Equation (2). In Equation (2), the axes aredifferent from those implied in Equation (1).

T ₁(y)=t ₀+(t _(max) −t ₀)[1−1.5(L _(wedge) −y)/L _(wedge)+(L _(wedge)−y)³/2L _(wedge) ³]  (2)

where:

-   -   t₀=thickness of wedge at the thin end=t_(kerf)−2t_(bondline)    -   t_(kerf)=nominal thickness of the kerf (as illustrated in FIG. 3        a)    -   t_(bondline)=nominal thickness of the bondline (about 0.005        inches)    -   t_(max)=maximum thickness of the wedge=0.9        (D_(max)−D_(throat))−4t_(bondline)    -   L_(wedge)=0.99 (L) (99% of the length of the cut, L_(cut)) (see        FIG. 3 a)    -   D_(max) is the same as defined for Equation (1)    -   D_(throat) is the same as defined for Equation (1)    -   y=distance from the thin end of the wedge piece.    -   Note that Equation (2) is the same for T₂(y), which is the        thickness of the other vane of the wedge, as shown in FIG. 5.

The width of the wedge, as defined in FIG. 5, is given by Equation (3),as follows:

W ₁(y)=W ₀+(W _(max) −W ₀)[1−1.5(L _(wedge) −y)/L _(wedge)+(L _(wedge)−y)³/2L _(wedge) ³]  (3)

where:

-   -   W₀=width of wedge at the narrow end (about 0.98        (D_(throat)))−2t_(bondline))    -   W_(max)=maximum width of wedge at wide end (about 0.95        (D_(max))−2t_(bondline))    -   t_(bondline)=nominal thickness of the bondline (about 0.005        inches)    -   L_(wedge)=0.99 (L) (99% of length of the cut, L_(cut)) (see FIG.        3 a)    -   D_(max)=the desired maximum diameter at the maximum width of the        wedge    -   D_(throat)=the diameter of the rod plus a clearance (typical        clearance being about 0.01 inches)    -   y=distance from the thin end of the wedge piece

Similarly to Equation (2), Equation (3) is the same for W₂(y), which isthe thickness of the other, relatively perpendicular vane of the wedge,shown in FIG. 5.

Thus, at the right-hand edge of the wedge (y=L_(wedge)), the wedgethickness is t_(max), and the wedge width is W_(max).

At the left-hand edge of the wedge (y=0), Equation (2) yields a value oft₀ for the wedge thickness, and Equation (3) yields a value of W₀ forthe wedge width. Thus, Equations (2) and (3) account for the fact thatthe wedge thickness, in practice, has a small non-zero value at its thinedge.

At the point where the thickness of the wedge becomes less than acertain small value, the wedge can be trimmed, so that the measuredthickness becomes the starting thickness of the wedge.

In the equations shown above, it is seen that the internal diameter ofthe fitting, and the thickness of the wedge, and the width of the wedge,all vary according to a third-order polynomial function of distancealong the axis of the joint.

The above equations represent only one of many possible embodiments. Inthe general case, the internal diameter of the fitting, and thethickness and width of the wedge, must vary smoothly and nonlinearlywith distance. Also, the contour or shape of the inside of the fittingshould be the same as the contour of the thickness of the wedge, whichshould be the same as the variation of the width of the wedge.

The desired maximum inner bore diameter of the fitting corresponding tothe end of the wedge (the right-hand side of the wedge in FIG. 2) isselected according to the following criteria:

1) the cross-sectional area of the fitting is at least twice thecross-sectional area of the rod at any point along the fitting which isoccupied by the wedge; and

2) the maximum diameter is greater than about 1.3 times the diameter ofthe rod and less than about 1.5 times the diameter of the rod.

Also, in practice, the maximum width of the wedge is not quite equal tothe full diameter of the fitting.

The wedge should be relatively short and compact. The length of thewedge is preferably less than five times the diameter of the rod,allowing for a shorter fitting that is less than 5.3 times the diameterof the rod.

In general, substantially all of the space within the fitting, at allpoints where the rod and wedge are present, is occupied by thecomponents of the invention, namely the wedge, the rod, and to a minimalextent, the adhesive. There is virtually no “air” or unoccupied spacewithin the fitting, where the rod is present.

The wedge preferably has a cruciform shape. FIGS. 3-5 illustrate thisfeature. The cruciform wedge is illustrated in the perspective view ofFIG. 5, which shows vertical vane 50 and horizontal vane 51. The vanescan be machined as a unitary part, or they could be separatelyconstructed and suitably joined. Both vanes have a thickness whichincreases from left to right, as shown in the drawing. The variation inthickness of each vane could be as given in Equation (2), discussedabove. If Equation (2) is used to define the variation of the thicknessof one of the vanes, it should be used for both vanes. In general, allvanes should have the same variation of thickness with distance alongthe wedge.

FIG. 3 shows the wedge 52 inserted within the rod 53. The end view ofFIG. 4 further illustrates the cruciform structure of the wedge, when itis embedded in the rod 53.

FIG. 3a shows the rod 53 having an opening or slit 55 formed therein.FIG. 3a represents the state of the rod before a wedge has beeninserted. The figure also indicates the definition of the quantityt_(kerf), which is the thickness of the kerf, which is the materialremoved from the rod in forming the slit. FIG. 4a shows thecorresponding end view of the rod of FIG. 3 a.

The wedge could have greater numbers of vanes. FIGS. 6 and 7 illustratean example in which the wedge comprises three vanes. The side view ofFIG. 6 shows two vanes 61, 62, and the end view shows all three vanes61, 62 and 63.

In the preferred embodiment, the wedge has at least two vanes. It isalso possible for the wedge to have only one vane. In this case, theswaging effect would occur in only one direction. This arrangement wouldresult in a weaker rod assembly, but might be useful in certainapplications.

In the above-described example, the internal diameter of the fitting,and the outer diameter of the rod, and the thickness of the wedge, varyaccording to the cube of the distance along the fitting. This curvatureneed not be exactly as shown in the example. Rather, it is a feature ofthe invention that the curvature be described by a polynomial equationhaving an order of at least two. Such equation may represent thedeflected shape of a cantilever beam under an end load. Thus, thediameter of the fitting could vary with the square or the cube, or somehigher power, of the distance.

It is important that the above-described curvature be smooth andcontinuous, and that the curvature continue along substantially all ofthe distance along which the rod is inserted into the fitting. Ifinstead the interior diameter of the fitting varied linearly withdistance (i.e. defining a conic shape), stress concentrations would format kinks in the fitting, causing weakening and eventual failure of thejoint. The curvature may be consistent with the deflected shape of abeam under distributed loads.

In making the joint of the present invention, a plurality of slits isformed in the rod, an adhesive is inserted in the slits, and applied tothe wedges, and the wedges are then inserted into the slits. The lengthof each slit should correspond to the length of the wedge to beinserted. In forming the slits, some of the material of the rod isremoved, this material being known as “kerf”. When the wedges are fullyinserted, substantially all of the space within the rod is filled. Moreparticularly, the wedges, when inserted, substantially conform to thecontour of the adjacent material of the rod, to insure that virtuallyall of the space is filled. The slits are very small relative to thediameter of the rod to not significantly weaken the rod.

The adhesive fills any small spaces or gaps that might remain betweenthe wedges and the rod, or between the fitting and the rod. The adhesivealso prevents the wedge from being forced out. It is possible to avoidthe use of an adhesive for this purpose if one has enough frictionbetween surfaces to hold the wedge in place.

In the preferred embodiment, the rod is a pultruded solid composite, andis compatible with high-temperature epoxy resins. The choice of a solidcomposite rod makes it feasible to use high-strength carbon or graphitefibers. Since the carbon or graphite fibers fill substantially all ofthe cross-sectional area of the rod (until the wedge has been inserted),the present invention takes advantage of the full cross-section, andresults in a stronger rod, for a given cross-sectional area. That is,the joint can accommodate loads of more than three times those of aconventional joint having the same size, such as the joint shown in U.S.Pat. No. 4,205,926.

The use of a solid rod contrasts with the use of stranded cables of theprior art. Cables inherently have spaces between strands, or betweengroups of strands, resulting in not all of the cross-sectional areabeing used in supporting a load.

The high strength of the rod makes it possible to design the joint suchthat the rod and fitting are of relatively small diameters. Thus, therod and fitting are more likely to be successfully operated within smalldiameter tubes, such as the bore of an oil well.

However, the invention is not limited to a rod or fitting of anyparticular diameter. What is important is that the rod initially be ofsolid construction, and that it initially have a constant diameter. Theinvention can be scaled such that larger and thicker rods and fittingscould be used.

Although the rod has been described as graphite, or as a composite ofgraphite and resin, the rod may be made of another material, such asmetal or fiberglass. The threaded end of the fitting allows multiplesegments to be connected using a standard coupling technique.

The joint of the present invention is intended to transfer large loadsin tension, but not compressive loads. The plug caps off the end of therod, and will withstand relatively small, incidental compression loadsthat might otherwise cause the rod to unseat from the fitting.

The present invention is not limited to use with sucker rods in the oilindustry. It could be used in structural applications such as tensionrods for pre-stressing of concrete and other materials which are strongin compression. It could be used in making guy wires or cables. It couldalso be used for pre-stressed concrete structures and/or in makingsuspension supports, such as are used for bridges.

The invention can be modified in various ways. As indicated above, thenumber of vanes of the wedge can be varied. The materials used for thewedge, the rod, and the fitting can be changed, consistent with therequirements of stiffness. The exact contour of the relevant surfaces ofthe fitting and wedge can be varied, as long as the contour is smoothand nonlinear.

FIGS. 8A, 8B, 8C and 8D sequentially depict the steps of the preferredmethod of the present invention. In FIG. 8A, the fitting 2 has beenpositioned within the chuck of the press machine used to assemble thejoint of the present invention. The rod 53 has been slid into thefitting 2 in direction “D” until the pre-determined end portion R(E) ofthe rod 53 is exposed beyond the threaded end 70 of the fitting 2. Thisdistance R(E) can be expressed as either a dimension, or as a lengththat is determined as a function of the diameter of the rod 53. Theoptimum exposed portion R(E) should be approximately 125 percent of thelength of the slit 55 (and wedge 52). As such, for 4-inch longslit/wedge, the optimum exposed portion R(E) is five (5) inches.

Prior to inserting the wedge 52 into the slit 55, the outer surfaces ofthe wedge(s) 52, inner surface of the fitting 2, and outer surface ofthe rod 53 are all coated with a thin layer of adhesive. This adhesivehas been observed to resist relative movement between the wedges, rodand fitting once the fitting has been pressed together (i.e. as depictedin FIG. 8D).

When applying the adhesive, a small volume fraction (<5%) of small, hardspheres (herein termed “bonding beads”) made from glass or metal areadded to the adhesive to maintain a minimum bond line thickness ofapproximately 0.007″ to prevent the adhesive from being scraped offduring the insertion process. Alternatively, small diameter glassfilaments or metal wires could be aligned lengthwise in the adhesive toserve the same function of ensuring the minimum bond line thickness.

Next, as depicted in FIG. 8B, the wedge 52 (or cruciform pair of wedgesas depicted in FIG. 4) is/are partially inserted into the slit 55 (orslits) until the pre-determined end portion W(E) remains exposed beyondthe face of the rod 72. This distance W(E) can be expressed as either adimension, or as a length that is determined as a function of thediameter of the rod 53. The optimum exposed portion W(E) should beapproximately ⅔rds of the length of the wedge 52 (and slit 55). As such,for a 4-inch long slit/wedge, the optimum exposed portion W(E) is 2 ⅔rdsinches.

In FIG. 8C, the wedge(s) face 74 and rod face 72 are being pulled indirection −D relative to the chuck of the joint press machine until theface of the rod 72 extends into the threaded portion 75 of the fitting 2by “pre-press exposed portion” W(E). It should be understood thattypically this position is reached (transitioning from the position ofFIG. 8B) by pulling on the rod 53 in direction −D (rather than byhandling the wedge(s) 52). This distance W(E) can be expressed as eithera dimension, or as a length that is determined as a function of thediameter of the rod 53. The optimum pre-press exposed portion W(E)should be approximately ⅔rds of the length of the wedge 52 (and slit55). As such, for a 4-inch long slit/wedge, the optimum exposed portionR(PE) is 2 ⅔rds inches.

Finally, FIG. 8D depicts the final positions of the wedges, rod andfitting after the joint has been pressed in direction −D by the pressmachine. After pressing, the rod 53 remains in the “rod seated position”P(F) relative to the end of the tapered portion 77 of the fitting 2, andthe wedge(s) is/are in “wedge seated position” with end of 74 in thesame plane as the end of the rod face 72.

The registration or positioning of the wedge(s) 52 relative to the rod70, and the rod 70 relative to the fitting 2 prior to the componentsbeing pressed together has been found to be extremely critical in theformation of a strong fitting. When positioned as detailed above, thepress device used to form the final joint will press down (in a singlepressing operation) on the wedge face 74 and the rod face 72 so that thewedge 52 arrives at its optimum position relative to the rod 53 just asthe rod 53 reaches its final position relative to the fitting 2. Thesefinal positions were determined after substantial testing to provide thestrongest joint between the rod 53 and the fitting 2 ever beforeassembled. If we now turn to FIG. 9, we can examine additional featuresof the steps depicted in FIGS. 8A-8D.

FIG. 9 is a flowchart showing the steps of the preferred method 80 ofthe present invention. It should be understood that the fitting [2] hasfirst been inserted into, and secured within the chuck of the jointpress machine. The rod [53] is inserted into the fitting [2] until theend is exposed by not less than dimension [R(E)] 100. Next (or at anytime prior to step 104), adhesive (e.g. epoxy) and bonding beads areapplied to the curved side face(s) of the wedge or wedges [52] 102.

Next, the wedge or wedges [52] are inserted into the slit(s) 55 formedin the end of the rod [52] until they are partially inserted 104 (i.e.until [W(E)]) is reached. Epoxy with bonding beads is then applied tothe exposed end (portion [R(E)]) of the rod [53] 106, and the rod [53]is then slid into the fitting [2] until it reaches pre-press position[R(PE)].

Finally, the wedge(s) [52] are pressed until they are seated intoslit(s) [55] in the rod [53], and the rod [53] is forced into thetapered section of the fitting [2] until it also reaches its seatedposition [P(F)]. The wedge(s) [52] will then also be in their seatedposition [P(F)]. The fitting is now completed and ready for attachmentto (a) another fitting [2], or (b) another structure via a threaded rodthreadedly engaging the threaded portion [75] of the fitting [2].

Those skilled in the art will appreciate that various adaptations andmodifications of the just-described preferred embodiment can beconfigured without departing from the scope and spirit of the invention.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention may be practiced other than as specificallydescribed herein.

What is claimed is:
 1. A joint, comprising: a) a fitting formed of asingle piece of a machined metal, the fitting having an interiorsurface, b) a solid rod having an end which is inserted at least partlyinto the fitting, c) the rod having an opening, the opening being insidethe rod and formed in said end, and d) a wedge being inserted into theopening of the rod, wherein the rod has an exterior surface whichsubstantially conforms to the interior surface of the fitting, whereinthere is less than 0.07 inches between the interior surface of thefitting and the exterior surface of the rod, wherein the interiorsurface of the fitting has an internal diameter which varies smoothlyand nonlinearly with distance along the fitting, wherein the wedge has adimension which varies smoothly and nonlinearly with distance along thewedge, and wherein a variation of the dimension of the wedge withdistance is substantially similar to a variation of the internaldiameter of the fitting with distance, wherein an axial end of the wedgeis substantially aligned with an axial end of the rod, and wherein theaxial end of the rod is substantially aligned with an axial end of theportion of said interior surface of the fitting wherein the diametervaries smoothly and nonlinearly with distance.
 3. The joint of claim 1,wherein the diameter of the fitting, and the dimension of the wedge,vary with at least a second power of the distance along the fitting orwedge, respectively.
 4. The joint of claim 1, wherein the wedge is madeof a material having high stiffness.
 5. The joint of claim 1, whereinthe fitting has a cross-sectional area and the rod has a cross-sectionalarea, and wherein the cross-sectional area of the fitting is at leasttwice the cross-sectional area of the rod.
 6. The joint of claim 1,wherein the wedge has a cross-sectional shape which is cruciform.
 7. Thejoint of claim 1, wherein the wedge includes at least two vanes whichare non-parallel to each other.
 8. The joint of claim 1, wherein thewedge has a length which is less than about five times a diameter of therod.
 9. The joint of claim 1, wherein the rod is solid except at saidopening.
 10. The joint of claim 1, further comprising a plug which isscrewed into the fitting such that the plug is positioned adjacent theend of the rod.
 11. A joint, comprising: a generally solid rod which isinserted into a fitting, the fitting being formed of a single piece of amachined metal, the rod having a slit, the slit being inside the rod, awedge being inserted into the slit, wherein the fitting has an insidesurface having a contour which varies smoothly and nonlinearly withdistance along the fitting, and wherein the wedge has a dimension whichhas a curvature similar to said contour, wherein the wedge tightlyengages the rod, and wherein the rod tightly engages the fitting,wherein the rod has an exterior surface which substantially conforms tothe inside surface of the fitting, wherein there is less than 0.07inches between the interior surface of the fitting and the exteriorsurface of the rod.
 12. The joint of claim 11, wherein said wedge andsaid fitting are made from metal and said rod is made from non-metallicmaterial, and further comprising a layer of adhesive material betweensaid fitting inside surface and said rod and said wedge that is not morethan 0.07 inches in thickness.
 13. The joint of claim 12, wherein saidadhesive material further comprises non-adhesive, uncompressibleelements that are between 0 and 0.02 inches in diameter.
 14. The jointof claim 13, wherein the wedge has a length which is less than aboutfive times a diameter of said rod.
 15. A joint, comprising: a generallysolid rod defined by an outer surface, said rod inserted into a fitting,the fitting being formed of a single piece of a machined metal, saidfitting defined by an internal bore having an inside surface whichvaries smoothly and nonlinearly with distance along the fitting, thecross-sectional shape of said inside surface defining a first contour,said first contour defined by a narrow end and an opposing wide end; therod having a slit, the slit being inside the rod; a wedge being insertedinto the slit, said wedge defined by at least two outwardly-facingsurfaces of matching shape, said shape of said outwardly-facing surfacesbeing said first contour; and an adhesive layer of not more than 0.07inches in thickness between said rod outer surface and said bore insidesurface.
 16. The joint of claim 15, wherein said wedge comprises fouroutwardly-facing surfaces of matching shape aligned in a cruciformshape.
 17. The joint of claim 15, defining a gap between said wedgeoutwardly-facing surfaces and said fitting inside surface, wherein thethickness of said gap is substantially consistent between said narrowend and said wide end of said fitting.
 18. The joint of claim 15,wherein said wedge is positioned within said fitting such that saidnarrow ends and said wide ends are aligned in relative juxtaposition.19. The joint of claim 15, wherein said adhesive layer is comprised of amixture of adhesive material and non-adhesive material, saidnon-adhesive material comprising non-compressible solid forms defined bydiameters of between 0 and 0.02 inches in diameter.